1. Field of the Invention
The present invention relates to a passive optical network (PON) system including an optical line terminal (OLT) and a plurality of optical network units (ONUs).
2. Description of the Related Art
An optical network is a technology that effectively provides a necessary band to a subscriber terminal. The optical network may have a point-to-point structure or a point-to-multipoint structure. An optical line terminal (OLT) may include an interface to support a plurality of optical network units (ONUs), and have control over the ONUs. In general, the point-to-point structure is used for an active optical network (AON), and the point-to-multipoint structure is used for a passive optical network (PON). Standardization on such structures is being conducted by international standardization organizations, such as the Institute of Electrical and Electronics Engineers (IEEE) and International Telecommunication Union-Telecommunication Standardization Sector (ITU-T).
Due to recognition of a necessity for power saving in a next generation optical network, the ITU-T achieved standardization with respect to two low power modes, a doze mode and a cyclic sleep mode, in G987.3 standards. The standardization relates to signaling between an ONU and an OLT, and state machine management. An optical transmitter and an optical receiver may be subject to power reduction. In the doze mode, an optical receiver of the ONU may be activated continually, and an optical transmitter of the ONU may be activated/deactivated (on/off) periodically. In the cyclic sleep mode, both the optical transmitter and the optical receiver may be activated/deactivated (on/off) periodically.
The OLT may register an ONU in an operation state through a registration process standardized in an ONU management control interface (OMCI) of G987.3 and G988. When conditions for transition to a sleep mode are satisfied, the ONU may operate in the sleep mode. The ONU may operate in a sleep mode set using an OMCI channel during the registration process, between the doze mode and the cyclic sleep mode. Events related to a transition to the sleep mode and a signaling method are described in G987.3.
Conventional standards describe a signaling message between an OLT and an ONU in a case of transitioning to a sleep mode and a normal mode to secure an intercompatibility between vendors, a definition of events, and a state machine. Based on signaling of a PON interval, an amount of power applied to an optical module of the ONU may be reduced.
In this example, there is a desire for a method of minimizing a delay time of upstream data and maximizing an effect of reducing an amount of power used by the ONU, by reducing an amount of time used for the transitioning of the ONU from the doze mode to the normal mode. Accordingly, a necessity for conducting research on various power saving schemes of reducing such power consumption is continuing to increase.